I think some form of sanctify would be great because it deals with sacred rituals and divinity. That would form a nice contrast with the necro mummy stuff that we have. It would put some of the attention on the other side of Egypt in pop culture, with images of golden temples and mystical priests.

However, I don't think that granting shroud for one turn is meaningful enough on its own. It's not like granting first strike or flying for one turn, where even a one-turn bonus could matter. The opponent could wait on removal, just cast something else, then remove the creature next turn. More importantly, if the opponent had sorcery removal and the creature was important, they would have cast it already. If it's instant removal, they would cast it in response to the sanctify.

To fix this, I wonder if it could be some kind of counter that stays on the creature. For example:

Temple Priest 1W
1/2 Priest (unc)
When ~ ETB, put a blessing counter on target creature.
W: Target creature you control with a blessing counter on it gains protection from the color of your choice until EOT.

Oasis Priest 1G
1/1 Priest (cmn)
When ~ ETB, put a blessing counter on target creature.
Creatures you control get +1/+1 for each blessing counter on them.

River Priest 2U
1/3 Priest (cmn)
When ~ ETB, put two blessing counters on target creature.
Creatures you control cost opponents 1 more to target for each blessing counter on them.

This is interesting. In a way, it's like a group-soulbond. Each of these creatures can induct others into a special group (without necessarily joining the group themselves) and grant bonuses to them, including those that joined the group earlier.

To nitpick, the Oasis Priest and River Priest above have the problem of being cumulative; for example if you played two Oasis Priests, each blessing counter would grant +2/+2. Also, some effects may require granting a lot of counters to start to be useful (like the pseudo-shroud one) but that may prove to be too strong when it's combined with another effect that is strong even when it grants just one counter (like the +1/+1 one).

It reminds me of graft creatures, who could grant abilities to other creatures with +1/+1 counters. If the set uses +1/+1 counters at all, that technology could be a good way to show blessings.

Temple Priest2 2W
1/2 Priest (unc)
When ~ ETB, put a +1/+1 counter on target creature.
W: Target creature you control with a +1/+1 counter on it gains protection from the color of your choice until EOT.

The concept behind Sanctify was to do a type of reverse detain - temporarily elevate one or more creatures and then synergize with the rest of your board. I chose shroud for a couple of reasons - to ensure that you don't sanctify the same creature once it has been sanctified, to strip away the number of combat tricks you can do with sanctified creatures to cut down board complexity and to play better with Edicts (an instant/sorcery subtype that grants global, non-targeted effects).

I don't think the shroud is integral to the mechanic though, but I would be careful about implementing sanctity counters as it made the board much more complex in my playtesting.